Subscriber terminal circuit for connecting an analog subscriber line to a digital switching center

Abstract

An interface circuit with integrated test functions relating to the subscriber line, with a test circuit realized in the simplest case by an ohmic resistance, and comprising a relay circuit having two changeover contacts by means of which in one switching position the leads of the subscriber line are connected with the interface circuit, and in the other switching position the subscriber line is disconnected and the test circuit is connected to the interface circuit.

We claim as our invention: 
     
       1. A method for operating a subscriber terminal circuit in a digital time-division multiplex telephone exchange, comprising the steps of: providing a subscriber terminal circuit with an interface circuit and a single multifunctional changeover relay, and providing said relay with two changeover contacts allowing connection to a test circuit and to leads of subscriber lines;   configuring said interface circuit to conduct test functions;   signaling said relay in response to a test request;   disconnecting said interface circuit from leads of a subscriber line that is connected to said interface circuit by utilizing said two changeover contacts of said relay;   connecting said interface circuit to a test circuit utilizing said two changeover contacts of said relay; and   executing said test functions within said interface circuit upon said test circuit.   
     
     
       2. The method of claim 1, further comprising: signaling said relay;   connecting said interface circuit to said leads of subscriber lines; and   executing said test functions upon said subscriber lines.   
     
     
       3. The method of claim 1, further comprising the steps of: signaling said relay;   connecting said interface circuit to said leads of subscriber lines; and   executing said test functions upon line leads of said subscriber lines.   
     
     
       4. A method for operating a subscriber terminal circuit in a digital time-division multiplex telephone exchange, wherein said subscriber terminal circuit comprises an interface circuit and a single multi-functional changeover relay, said relay having two changeover contacts allowing connection to a test circuit and to leads of subscriber lines, and said interface circuit having test functions, said method for operating said subscriber terminal circuit comprising the steps of: monitoring said subscriber lines for a condition of impermissibly high interference voltages;   signaling said single relay in response to said condition;   disconnecting said interface circuit from leads of a subscriber line that is connected to said interface circuit by utilizing said relay's two changeover contacts;   connecting said interface circuit to a test circuit utilizing said relay's two changeover contacts.     
     
     
       5. A method for operating a subscriber terminal circuit in a digital time-division multiplex telephone exchange, wherein said subscriber terminal circuit comprises an interface circuit and a single multi-functional changeover relay, said relay having two changeover contacts allowing connection to a test circuit and to leads of subscriber lines, and said interface circuit having test functions, said method for operating said subscriber terminal circuit comprising the steps of: signaling said single relay prior to a deactivation of an entire group of subscriber terminal circuits from a main distributor;     disconnecting said interface circuit from leads of a subscriber line that is connected to said interface circuit by utilizing said relay's two changeover contacts; connecting said interface circuit to a test circuit utilizing said relay's two changeover contacts.     
     
     
       6. The method of claim 4, wherein said test circuit comprises a single resistor. 
     
     
       7. The method of claim 4, wherein said test circuit comprises a passive network with complex resistance behavior. 
     
     
       8. The method of claim 5, wherein said test circuit comprises a single resistor. 
     
     
       9. The method of claim 5, wherein said test circuit comprises a passive network with complex resistance behavior. 
     
     
       10. A method for operating a subscriber terminal circuit in a digital time-division multiplex telephone exchange, comprising the steps of: providing a subscriber terminal circuit with an interface circuit and a single multi-functional changeover relay, and providing said relay with two changeover contacts allowing connection to a test circuit and to leads of subscriber lines;   configuring said interface circuit to conduct test functions;   signaling said relay in response to a test request;   disconnecting said interface circuit from leads of a subscriber line that is connected to said interface circuit by utilizing said two changeover contacts of said relay;   connecting said interface circuit to a test circuit utilizing said two changeover contacts of said relay; and   executing said test functions within said interface circuit upon said test circuit; and   wherein said test circuit comprises a single resistor.   
     
     
       11. The method of claim 1, wherein said test circuit comprises a passive network with complex resistance behavior.